Electronic engine control systems typically respond to sensed conditions, such as engine speed and load, operating temperatures and pressures, accelerator position, and exhaust oxygen levels, in order to properly adjust ignition timing and the rate at which fuel and air are delivered to the engine. Electronic control systems can significantly improve engine efficiency while minimizing undesired exhaust emissions under changing operating conditions.
Such multifunction electronic engine control systems are preferably implemented with integrated circuit microcontrollers operating under stored program control. Suitable microcontrollers are available from a variety of sources and include the devices described in Motorola's Microcontroller and Microprocessor Families, Volume 1 (1988), published by Motorola, Inc., Microcontroller Division, Oak Hill, Tex.
The microcontroller in an electronic engine control generates timed output control signals which operate the engine's electronic ignition and fuel injection systems. These control signals are typically synchronized by event signals from one or more sensors which indicate crankshaft position. Commonly called PIPS (Piston Interrupt Signals), these position sensing signals typically initiate microcontroller interrupt-handling routines to perform a variety of control functions synchronized to the engine's rotation. In addition, the microcontroller processes additional analog signal values from other sensors which are converted into digital quantities by analog-to-digital (A-D) converters within the microcontroller.
Electronic engine control systems perform elaborate control functions by processing available digital values which describe the engine's operating condition to vary control inputs which determine the engine's operation. Increasingly sophisticated mechanisms may accordingly be implemented at little additional manufacturing cost to optimize engine performance over a wide range of operating conditions.
The engine control system typically varies the timing of ignition with respect to piston motion to enhance engine performance. Normally, spark timing is adjusted uniformly for all cylinders, varying the time of ignition with respect to the top-dead-center position of the firing cylinder to optimize performance. Although electronic control systems include instrumentalities that may be readily adapted to provide cylinder-by-cylinder control of spark timing in order to equalize burn-rates or to retard the spark for knock-prone cylinders, these techniques are unnecessary for well-designed and well-maintained engines. Cylinder-by-cylinder ignition timing control can, however, yield significant benefits in other ways by following the principles of the present invention.